When both bit data and word data are handled in a conventional programmable controller (hereinafter abbreviated to a "PCS"), it has heretofore been general practice to handle them separately from each other or handle word data as a set of pieces of bit data irrespective of whether the system is a small-scale PCS or a large-scale PCS. Thus, no consideration has heretofore been taken to facilitation of programming and simplification of the circuit configuration.
In the conventional programming, it is general practice to set an area for outputting bit data and an area for outputting word data separately from each other. This conventional method suffers, however, from the following problem. Since each of the above-described areas is determined in advance, it is impossible to cope with a change in the ratio in size between bit data memory area and word data memory area which may occur due to the difference between users' programs. Accordingly, it is impossible with the above-described conventional method to satisfy a specification demanded by each individual user. In addition, when the program is changed, after a PCS has been delivered to a user, so that the amount of bit data or word data is excessively large, such data cannot be accommodated in a predetermined area, which means that it is impossible to store the program, disadvantageously.
It should be noted that examples of prior arts related to the device of the type described above include those disclosed in Japanese Patent Laid-Open Nos. 57111/1981 and 23110/1982.